The field of this invention relates to a new vapor phase catalytic conversion of aromatic esters to aromatic aldehydes. As literature reports, previous attempts to prepare aromatic adlehydes directly from aromatic esters involve the use of complex metal reducing agents such as sodium aluminum hydride (Zakharkin, L. I., Garrilenko, V. V., Maslin, D. N., and Khorlina, I. M., Tetrahedron Lett., 29, 2087 (1963)), sodium bis(2-methoxyethoxy) aluminum hydride (Vit., J., Org. Chem. Bull., 42, 1 (1970)), and diisobutylaluminum dihydride (Zakharkin, L. I., and Khorlina, I. M., Tetrahedron Lett., 14, 619 (1962)). These reductions require long reaction times (5 to 7 hours) and temperatures ranging from -45.degree. to -70.degree.C. High yields of aromatic aldehydes are generally not achieved, as the aldehyde undergoes a Tishchenko-type condensation catalyzed by the metal reducing agent (Zakharkin, L. I., and Sorokina, L. P., Zh. Obshch. Khim., 37, 561 (1967)).
In contrast to this, we have discovered that when an aromatic ester, wherein the portion of the ester group derived from the alcohol has no .beta.-hydrogens, is heated in the vapor phase to a temperature in excess of 400.degree.C and is passed over an alumina catalyst at essentially ambient pressure for as short a time as 3 seconds, the corresponding aromatic aldehyde will be produced as the dominant product.